A holding device for machine tools is disclosed in DE 39 06 822 C3 (corresponding to U.S. Pat. No. 5,035,545). With this conventional holding device, a spreading key is provided having spreading body with an elliptical cross-sectional profile. The receptacle for the spreading body in the slot of the cutting tool carrier has two recesses facing one another in the edges of the slot. The recesses correspond to the two small apex curvature circles of the elliptical cross-sectional profile outline of the spreading body. Due to the precise correspondence of the relevant apex curvature circles required for safe and secure functioning of the known holding device, the spreader key and the cutting tool carrier are costly to manufacture. This costly manufacture is a drawback, and is required principally because of the narrow manufacturing tolerances which need to be maintained to attain the precise correspondence.